1. Technical Field
The present invention relates to a stripe noise correction method of a captured image, a photographing apparatus and an electronic endoscopic apparatus.
2. Related Art
A solid-state imaging device (an image sensor) for photographing a color image includes a plurality of pixels (photo-diodes) arranged on a semiconductor substrate in a two-dimensional array type. And, in the solid-state imaging device, a color filter is stacked on each of the pixels, and, for example, an amplifier or an analog/digital (A/D) convertor is provided in each pixel column.
It is difficult to manufacture the amplifiers or the like, each of which is installed in the corresponding pixel column, to have the same performance, and a fluctuation in manufacture may occur. For this reason, a vertical stripe noise caused by the fluctuation in manufacture of the amplifiers or the like overlaps with a captured image of a subject. Since the vertical stripe noise deteriorates the image quality when the vertical stripe noise exists in a captured image, a correction processing is performed to reduce the vertical stripe noise. Although this example is described with the vertical stripe noise, a transverse stripe noise occurs when an amplifier or the like is provided in each pixel row. Although descriptions below are made with respect to the vertical stripe noise, the descriptions will be equally applied to the transverse stripe noise.
Since a vertical stripe noise is a fixed pattern noise, an inherent vertical stripe noise component of a solid-state imaging device may be calculated in advance. When a subject is captured, the vertical stripe noise correction may be performed by subtracting the vertical stripe noise component from a real detection signal of each of the pixels. However, since the vertical stripe noise correction is performed in a digital signal processing, a portion below the decimal point of the vertical stripe noise component cannot be removed. Accordingly, a quantization error occurs. That is, the quantization error remains as a narrow vertical stripe noise.
As disclosed in Patent Document 1 (JP-B-4396757) and Patent Document 2 (JP-A-2005-167918) in the related art, the vertical stripe noise correction includes a processing performed in which an artificial random noise is added such that an error equal to or less than a quantization accuracy (vertical stripe noise) is made less noticeable. In Patent Document 2, the ratio of adding the random noise is controlled on the basis of the magnitude of the quantization error.